Pneumatic elevators for lifting granular solids



United States Patent Inventor Pierre Ledent Parc de Sainval, Tilfl,Belgium Appl. No. 741,743 Filed July 1,1968 Patented Dec. 1, 1970Priority July 12, 1967 Belgium No. 701,295

PNEUMATIC ELEVATORS FOR LIFIING GRANULAR SOLIDS 5 Claims, 2 DrawingFigs.

US. Cl 263/21, 34/57 int. Cl. F27b 15/00 Field of Search 263/ 19(B),21(A); 34/57(A), 57(T) FUN [56] References Cited UNITED STATES PATENTS3,030,089 4/ 1962 Johnson, Jr 263/21A 3,373,504 3/1968 Mclntire et al.34/5 7A Primary Examiner-John J. Camby Attorney-Jacob L. KollinABSTRACT: Apparatus for the pneumatic elevation of granular solidproducts utilising a compressed carrier gas, comprising a closedreceptacle the bottom of which is constituted by a porous surface,through which a gas may be blown at such a speed as to fluidize a bed ofgranular solids situated in said receptacle when the apparatus is inuse, and a vertical elevator tube passing through the top wall of saidreceptacle and extending inside it, wherein means are provided forintroducing a flow of high-temperature gas into said receptacle outsidethe elevator tube.

Paiited Dec. 1, 1970 3,544,089

I fag. 2

INVENTOR 519915 1605A? ATTORNEY PNEUMATIC ELEVATORS FOR LIFTING GRANULARSOLIDS various devices for the transport and pneumatic elevation ofsolid granular substances are known. In installations of this type, therate of flow is generally high, above 20 to 25 meters per second, andthe ratio between the feeds by weight of solid end carrier gas isgenerally low, more often of the order of 2 and more rarely from 8 to10.

Such installations may function below atmospheric pressure but in thatcase the solid gas ratio is very low and the installation must compriselarge fans and vast filtering devices for refining the carrier gas. Oneway also have recourse to a compressed carrier gas but there is then theproblem of introducing the solid into the said carrier gas; this problemis solved by relatively complicated mechanical devices, such as sieves,screws or honeycombed sluices.

An apparatus for the pneumatic elevation of granular solid products,utilizing a compressed carrier gas and previously imagined by theapplicant, comprises two receptacles communicating with one another attheir lower part, the bottom of the said two receptacles beingconstituted by a porous surface, through which a gas may be blown atsuch a speed as to fluidize two intercommunicating beds of granularsolids situated in the two receptacles when the apparatus is in u'se, inwhich the first receptacle acting as a feeding device is open at itsupper part so that it may contain fluidized bed, the surface of which isat atmospheric pressure, and the second receptacle is a closedreceptacle through the roof of which pass one or more vertical tubescapable of acting as a pneumatic elevator.

This apparatus can be employed simultaneously as a pneumatic elevatorand as a heat exchanger in which heatexchange takes place between thecarrier gas and the granular solids. However, since the gas isintroduced through the porous surface acting as the base of thefluidized bed, the temperature at which the gas can be introduced islimited to the temperature which can be tolerated by the material ofwhich said porous surface is composed.

The apparatus of the present invention enables this dra back to beovercome and is characterized by the fact that the quantity of gasintroduced through the porous surface acting as the base of thefluidized bed is limited to the absolute minimum which is necessary toensure fluidization of the granular solids, and that another flow of gasat a higher temperature is introduced above the level of the fluidizedbed.

The total gas flow rises up through the vertical elevator tube or stack,which acts as a heat exchange by creating direct contact between the hotgases and the granular solids.

The effective cross section of the vertical elevator tube is generallyso selected that the speed of circulation of the rising gases does notexceed a level of between 10 and 15 meters per second. this limitationon the speed of circulation increases the time during which the solidsand the gases are in contact and this, of course, promotes heattransfer. Moreover, it also reduces the power consumption of and therate of wear in the installation.

ln high-capacity installations, operating at elevated temperatures, itmay be necessary or desirable to employ an elevator tube of very largediameter which will result in a reduction in the amount of heat transferbetween the gas flowing up the tube and the granular solids, the latterpreferably following a boundary layer close to the tube wall. In suchcases as this, to overcome this disadvantage, it is generallyadvantageous to employ an elevator stack comprising two or moreconcentric tubes, the central tube being sealed at .at least the lowerend thereof and the annular space or spaces between the said tubes beingthe only space utilized for the circulation of the gases and solids.

Since the elevator stack operates as a concurrent heat exchanger, thetemperature of the gas leaving the tube is always slightly higher thanthe temperature of the solids. In order, therefore, to improve thethermal efficiency of the system, it is generally advantageous toinclude a waste-heat recovery system which can be used for air heatingpurposes and possibly to heat the gas which is used for the heatingfunction and for the fluidization.

The invention is further illustrated with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic sectional view of one embodiment of theapparatus of the present invention, and

H6. 2 is a section along line ll-ll of H6. 1.

The apparatus illustrated comprises an assembly of two associatedreceptacles l and 2 communicating with one another at their lower partsthrough an opening 3. I

The bases of these receptacles are in each case constituted by a poroussurface 4 which may be a porous slab or any other appropriate kind ofdiffuser arrangement such as a perforated plate or grid of refractorysteel. 7

The receptacle 2, all the internal walls of which are lined with arefractory material, communicates with a burner 5 which produceshigh-temperature gases; these gases are in troduced into the receptacle2 above the surface of the fluidized bed and are evacuated through theelevator tube 6 which also acts as a heat exchanger between the gasesand the granular product. The elevator device comprises two concentrictubes of which the central one 7, sealed at its bottom end, the annularspace between the two tubes being the sole space employed for thecirculation of the gases and the solid materi-' als.

At the top end of the elevator device, the gases and the solids areseparated in chamber 8. The granular solid material is evacuated acrossa screen and the gases are discharged through a flue after having passedthrough a heat exchanger 9 which preheats the air, compressed by the fan10, used to produce the hot gases and to fluidize the bed of solidgranular material contained in the receptacles l and 2.

An installation of this kind enables a granular solid to be heated totemperatures in the order of 800 C. with an overall thermal efficiencyof as much as 80 percent. The power consumed in lifting the granulatedsolids is very low as a result of the fact that the air compressiontakes place at ambient temperature but the air used for the lifting isat high temperature. By way of example, in an installation designed tolift fine sand through a height of 8 meters, reaching a finaltemperature of 800 C., the power taken by the fan increases by only Ikw. for an increase in sand throughput from 20 to 40 metric tons perhour.

In certain industrial applications, it may be desirable to employ forthe heating function residual gases (stack gases, exhaust gases etc. thepressure of which is insufficient to permit operation of theinstallation in the manner described. In cases of this kind, the deviceis supplemented by the fan 11 located beyond the exchanger 9, in orderto produce a forced draught in the system.

lclaim:

1. an apparatus for the pneumatic elevation of granular solid productsutilizing a compressed carrier gas, comprising' a closed receptacle thebottom of which is constituted by a porous surface, through which a gasmay be blown at such a speed as to fluidize a bed of granular solidssituated in said receptacle when the apparatus is in use, and a verticalelevator tube passing through the top wall of said receptacle and ex-;

tending inside it, wherein means are provided for introducing t a flowof high-temperature gas into said receptacle outside the elevator tubeabove the fluidized bed.

2. an apparatus according to claim 1, wherein said means for introducingthe flow of high-temperature gas comprise one or more gas burners or oilburners located in a vertical wall of said receptacle.

3. an apparatus according to claim 1, wherein said elevator tubecomprises at least two concentric tubes, the centre one of said tubesbeing sealed at at least its lower end.

4. an apparatus according to claim 3, in which said elevator tubecomprises two concentric tubes only.

5. an apparatus according to claim 1, wherein the air and possiblyalsothe gas, used to supply the burner or burners and to producefluidization in the vessel, is/are preheated in a heat exchanger byrecovery of the heat still contained by the gases which have been usedto raise the solid product. I

